The following relates generally to wireless communication, and more specifically to uplink listen-before-talk (LBT) operation.
Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems, (e.g., a Long Term Evolution (LTE) system). A wireless multiple-access communications system may include a number of base stations, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE).
In some cases, a user equipment (UE) operating in shared or unlicensed spectrum may perform a listen-before-talk (LBT) procedure, which may include as a clear channel assessment (CCA) or enhanced clear channel assessment (eCCA) to determine whether the channel is available for communication. If a UE and a base station both use LBT, uplink transmission opportunities may be limited. For example, a base station may perform a CCA to send an uplink grant to a UE in an unlicensed carrier; the UE may then perform another CCA to transmit the corresponding uplink message associated with the uplink grant. Each CCA performed may introduce the possibility of delay or disruption.